One Thing in Common

[Estanesse]

They all came to aid a friend or people who were friendly towards them

Beren Attacked the dwarfs because they killed Thingol and to (I think) prevent them from doing more damage in Doriath;
Turin Killed Glaurung and so prevent him from destroying Brethil;
Aragorn came to the aid of Minas Tirith;
Eomer came to the aid of Minas Tirith;
Turgon Came in what looked as a decisive moment to the aid of Finrod and co;